Field of the Invention
The present invention relates to weighing instruments of the kind having a number of graduated scales for indicating weight related characteristics of selected materials such as the caloric content of selected food items.
As it is well known, it is often necessary to determine the caIoric content of various kinds and quantities of common food items, either for regular dieting to maintain good health and fitness, or for following a rigid diet established by a physician for the treatment of an illness or deficiency. Special diets may also require the determination of other weight-related characteristics of foods, such as the content of protein, fat, carbohydrates, and minerals such as calcium, phosphorous, iron, and sodium. Diabetics, for example, must pay particular attention to their intake of carbohydrates (glucides).
The basic method of determining a weight related characteristic of an unknown quantity of a food item is to weigh the food item, refer to a table or listing of foods to obtain the characteristic for a unit weight of the particular kind of food item, and multiply the unit weight characteristic by the weight of the food item. The unit weight characteristics of food items have been determined by the U.S. Department of Agriculture, and compilations have been published by numerous authors, including C.F. Adams, Encyclopedia of Food and Nutrition, Drake Publishers, Inc., New York, N.Y. (1977), and B.L. Gelb, The Dictionary of Food, Paddington Press Ltd., New York, N.Y. (1978).
It has been recognized that the steps of referring to the table of food characteristics and multiplying by the unit weight characteristic could be avoided by weighing the food item on a scale having a number of graduated scales, each of which corresponds to a different food item. Due to the limited number of graduated scales that can be handled, however, it has been necessary to associate each graduated scale with a number of food items. A small number of graduated scales can be used, each corresponding to a different unit weight characteristic, but then a table or listing is needed for referencing each food item to a particular one of the graduated scales.
Another known method of reducing the number of graduated scales is to provide a single respective scale for each of a plurality of food groups. This method assumes, however, that the unit weight characteristics of the foods in each group are not substantially different, which is not always true.
In German utility model No. 73 42204, a weighing instrument is described whose double pointer is moved in front of a fixed scale expressed in weight and behind a flexible transparent card slideable in horizontal slideways which give it the shape of a cylindrical sector. This card carries successive graduated scales which relate to different categories of foods and which are expressed in calories. Such a card is vulnerable since it slips out of the slide at its two ends and it is thus exposed to shocks, which risk damaging it and/or causing it to pass inadvertently from one category of foods to another, as well as to splashes of materials which are liable to soil it. In addition, the horizontal dimensions of the card are necessarily restricted, which limits the maximum number of categories of foods to a low figure.
In U.S. Pat. No. 4,119,162 a weighing instrument is described having a pointer rotating coaxially with respect to a flat annular dial whose angular position is adjustable by the user and which is divided into four sectors. One of these sectors extends over an angle of 180.degree. and is graduated only by weight. Each of the three other sectors extends over an angle of 60.degree. and comprises three or four concentric scales whose external graduation is expressed in weight and of which each of the other graduations is expressed in calories for one category of foodstuffs. The scales are labelled merely by letters A-H, which could cause confusion when reading the scales since a table is required for associating the food groups with the letters. A known alternative is to place the names of representative food items next to their associated scales, but this further limits the space available for the scales.
In U.S. Pat. No. 4,223,750 a weighing instrument is described having a scroll carrying a large number of scales calibrated for groups of foods having similar characteristics and labeled by the names of representative food items in each group. To select the scale for a desired food item, the operator must turn the scrolls, by hand or by operating an electric motor, until the scale for the food item comes into view.